Patent application title: Terephthalic Acid Composition and Process for the Production Thereof

Abstract:

Terephthalic acid is prepared by reacting a 2,5-furandicarboxylate with
ethylene in the presence of a solvent to produce a bicyclic ether; and
then dehydrating the bicyclic ether. The process of the present invention
effectively produces terephthalic acid, while reducing or eliminating the
impurities, color bodies and carbon oxides produced in commercial
practice by the liquid-phase oxidation of methyl-substituted benzene
feedstocks.

Claims:

1. A terephthalic acid composition prepared by the steps comprising:a.
reacting a 2,5-furandicarboxyate with ethylene in the presence of a
solvent to produce a bicyclic ether; andb. dehydrating the bicyclic
ether.

2. The composition of claim 1 wherein the 2,5-furandicarboxylate is
derived from biomass.

3. The composition of claim 2 wherein the 2,5-furandicarboxylate is
derived from biomass by the steps comprising:a. converting the biomass to
a sugar comprising fructose, sucrose and mixtures thereof;b. converting
the sugar to 5-hydroxymethylfurfural; andc. oxidizing the
5-hydroxymethylfurfural to 2,5-furandicarboxylate.

4. A terephthalic acid composition comprising a minor amount of
2,5-furandicarboxylic acid as an impurity wherein the terephthalic acid
has a ratio of carbon-14 isotope to carbon-12 isotope of about
1.5.times.10.sup.-12 to 1.

5. The composition of claim 4 wherein the amount of 2,5-furandicarboxylic
acid is less than about 25 ppm.

6. A terephthalic acid composition having a purity sufficient for direct
conversion by reaction with at least one glycol to polyester suitable for
the manufacture of fiber and film without additional purification
comprising less than about 25 ppm of 2,5-furandicarboxylic acid as an
impurity.

7. The composition of claim 6 wherein the terephthalic acid has a ratio of
carbon-14 isotope to carbon-12 isotope of about 1.5.times.10.sup.-12 to
1.

Description:

FIELD OF THE INVENTION

[0001]This invention relates generally to terephthalic acid and, more
particularly, to a new terephthalic acid composition and a process for
the production of terephthalic acid from a 2,5-furandicarboxylate.

BACKGROUND OF THE INVENTION

[0002]Terephthalic acid and other aromatic carboxylic acids are widely
used in the manufacture of polyesters, commonly by reaction with ethylene
glycol, higher alkylene glycols or combinations thereof, for conversion
to fiber, film, containers, bottles and other packaging materials, and
molded articles.

[0003]In commercial practice, aromatic carboxylic acids are commonly made
by liquid-phase oxidation in an aqueous acetic acid solvent of
methyl-substituted benzene and naphthalene feedstocks, in which the
positions of the methyl substituents correspond to the positions of
carboxyl groups in the desired aromatic carboxylic acid product, with air
or another source of oxygen, which is normally gaseous, in the presence
of a bromine-promoted catalyst comprising cobalt and manganese ions. The
oxidation is exothermic and yields aromatic carboxylic acid together with
high- and low-molecular weight byproducts, including partial or
intermediate oxidation products of the aromatic feedstock, and acetic
acid decomposition reaction products, such as methanol, methyl acetate,
and methyl bromide. Water is also generated as a byproduct. Aromatic
carboxylic acids, typically accompanied by oxidation byproducts of the
feedstock, are commonly formed dissolved or as suspended solids in the
liquid-phase reaction mixture and are commonly recovered by
crystallization and solid-liquid separation techniques.

[0004]The exothermic oxidation reaction is commonly conducted in a
suitable reaction vessel at elevated temperature and pressure. A
liquid-phase reaction mixture is maintained in the vessel and a vapor
phase formed as a result of the exothermic oxidation is evaporated from
the liquid phase and removed from the reactor to control reaction
temperature. The vapor phase comprises water vapor, vaporized acetic acid
reaction solvent and small amounts of byproducts of the oxidation,
including both solvent and feedstock byproducts. It usually also contains
oxygen gas not consumed in the oxidation, minor amounts of unreacted
feedstock, carbon oxides and, when the oxygen source for the process is
air or another oxygen-containing gaseous mixture, nitrogen and other
inert gaseous components of the source gas.

[0005]The high temperature and pressure vapor phase generated by the
liquid-phase oxidation is a potentially valuable source of recoverable
acetic acid reaction solvent, unreacted feed material and reaction
byproducts, as well as energy. However, its substantial water content,
high temperature and pressure and corrosive nature due to components such
as gaseous methyl bromide, acetic acid solvent and water pose technical
and economic challenges to separating or recovering components for
recycle and recovering its energy content. Further, impurities that
remain unseparated in recovered process streams can prevent re-use of
streams if impurities adversely affect other process aspects or product
quality.

[0006]Purified forms of aromatic carboxylic acids are usually favored for
the manufacture of polyesters for important applications, such as fibers
and bottles, because impurities, such as the byproducts generated from
the aromatic feedstocks during oxidation and, more generally, various
carbonyl-substituted aromatic species, are known to cause or correlate
with color formation in polyesters made from the acids and, in turn,
off-color in polyester converted products.

[0007]Preferred purified forms of terephthalic acid and other aromatic
carboxylic acids with lower impurities contents, such as purified
terephthalic acid or "PTA", are made by catalytically hydrogenating less
pure forms of the acids, such as crude product comprising aromatic
carboxylic acid and byproducts generated by the liquid-phase oxidation of
the aromatic feedstock or so-called medium purity products, in solution
at elevated temperature and pressure using a noble metal catalyst.
Purification not only removes impurities from the crude and medium purity
products, particularly the major impurity, 4-carboxybenzaldehyde, but
also reduces the level of color bodies and the amount of metals, acetic
acid and bromine compounds. In commercial practice, liquid-phase
oxidation of alkyl aromatic feed materials to crude aromatic carboxylic
acid and purification of the crude product are often conducted in
continuous integrated processes in which crude product from liquid-phase
oxidation is used as the starting material for purification.

[0008]Reducing or eliminating the production of impurities, color bodies
and carbon oxides from such commercial processes continues to be an
ongoing challenge. One solution may be found in an alternative process
for the manufacture of aromatic carboxylic acids from feedstocks other
than methyl-substituted benzene and naphthalene feed materials.

[0009]The U.S. Department of Energy ("DOE") has recently identified 12
top-tier chemical building blocks from biomass processing, as reported in
the Biomass Report for the DOE Office of Energy Efficiency and Renewable
Energy entitled Top Value Added Chemicals from Biomass, Volume 1--Results
of Screening for Potential Candidates from Sugars and Synthesis Gas,
August 2004. Among the twelve building blocks identified by the DOE is
2,5-furandicarboxylic acid. The DOE has been soliciting proposals for the
use of 2,5-furandicarboxylic acid in the production of commodity
chemicals, such as polyesters.

[0010]It is generally known that biomass carbohydrates can be
enzymatically converted to fructose and other sugars. Under facile
dehydration conditions, these sugars are then converted to
5-hydroxymethylfurfural, which is readily oxidized to
2,5-furandicarboxylic acid. It has been reported that of the
approximately 200 billion tons of biomass produced per year, 95% of it is
in the form of carbohydrates, and only 3 to 4% of the total carbohydrates
are currently being used for food and other purposes. Thus, there is an
abundant untapped supply of biomass carbohydrates, which can potentially
be used for the production of non-petroleum based commodity chemicals
that are fully renewable.

[0011]Accordingly, it would be desirable to provide a process for the
production of terephthalic acid from a feedstock other than a
conventional alkyl aromatic feed material, such as paraxylene, which not
only reduces or eliminates the production of impurities, color bodies and
carbon oxides, but also eliminates the need for the purification step in
current commercial processes. It would also be desirable if the
alternative feedstock utilized in the process was derived from biomass.

SUMMARY OF THE INVENTION

[0012]The process of the invention, in its embodiments and features, calls
for reacting a 2,5-furandicarboxylate with ethylene in the presence of a
solvent to produce a bicyclic ether; and then dehydrating the bicyclic
ether.

[0013]In one embodiment of the invention, the 2,5-furandicarboxylate is
derived from biomass whereby enzymatic or microbial degradation occurs
from biomass carbohydrates to produce fructose, sucrose and mixtures
thereof, the sugars are then converted to 5-hydroxymethylfurfural, and
the 5-hydroxymethylfurfural is readily oxidized to
2,5-furandicarboxylate.

[0014]The inventive process efficiently and effectively produces
terephthalic acid with purity comparable to conventional PTA purified by
hydrogenation of crude product from paraxylene oxidation, while reducing
or eliminating the resultant impurities, color bodies and carbon oxides
produced in commercial practice by the liquid-phase oxidation of
methyl-substituted benzene feedstocks.

[0015]In another aspect, the invention provides a terephthalic acid
composition comprising a minor amount of 2,5-furandicarboxylic acid as an
impurity wherein the terephthalic acid has a ratio of carbon-14 isotope
to carbon-12 isotope of about 1.5×10-12 to 1.

[0016]The invention also provides a terephthalic acid composition having a
purity sufficient for direct conversion by reaction with at least one
glycol to polyester suitable for the manufacture of fiber and film
without additional purification comprising less than about 25 ppm of
2,5-furandicarboxylic acid as an impurity.

DETAILED DESCRIPTION OF THE INVENTION

[0017]The present invention is directed to a process for producing
terephthalic acid (TA) and to a new TA composition. In accordance with
this invention, a 2,5-furandicarboxylate is reacted with ethylene in the
presence of a solvent to produce a bicyclic ether, and then the bicyclic
ether is dehydrated. The resultant TA has a purity comparable to
conventional PTA purified by hydrogenation of crude product from
paraxylene oxidation and sufficient for direct conversion to fiber and
film.

[0018]In accordance with one embodiment, the 2,5-furandicarboxylate is
derived from biomass. "Biomass" is generally defined as plant material,
vegetation or agricultural waste used as a fuel or energy source. The
ratio of carbon-14 isotope to carbon-12 isotope for biomass carbon is
generally known to those skilled in the art to be about
2×10-12 to 1 based on the current natural abundance of
carbon-14 to carbon-12 as taken from air samples.

[0019]When 2,5-furandicarboxylate derived from biomass is utilized in the
practice of the invention, the resultant TA will have a ratio of
carbon-14 isotope to carbon-12 isotope of about 1.5×10-12 to
1, or 12 disintegrations per minute per gram of carbon, as measured on a
Geiger counter.

[0020]Furthermore, unlike conventional PTA produced from an alkyl aromatic
feedstock derived from petroleum refining, the TA composition derived
from biomass in accordance with the present invention contains a minor
amount of 2,5-furandicarboxylic acid (FDCA) as an impurity and is free of
contaminants, such as 4-carboxybenzaldehyde, and color bodies. The amount
of FDCA present in the TA composition derived from biomass is typically
at least about 10 ppm, as determined by high pressure liquid
chromatography. The maximum amount of FDCA in the TA composition is
preferably less than about 25 ppm. It is desirable to limit impurities in
TA compositions that are to be used in the manufacture of polyester to
avoid altering the physical or mechanical properties. Thus, if desired,
the FDCA impurity level can be reduced by crystallization with a solvent
such as water. The inventive TA composition, however, has a purity
sufficient for direct conversion by reaction with at least one glycol to
polyester suitable for the manufacture of fiber and film without the need
for any additional purification.

[0021]In one aspect of the current invention, the 2,5-furandicarboxylate
that may be used is FDCA. It is generally known to those skilled in the
art that enzymatic or microbial degradation occurs from biomass to
produce a mixture of fructose and sucrose. Biomass can also be converted
to sugars by a two-stage hydrolysis process as described in U.S. Pat. No.
4,427,453, which is incorporated herein by reference. In the first stage,
the biomass is crushed and treated with dilute mineral acid at a
temperature of about 135° C. to 190° C. under a pressure
sufficient to maintain a liquid mixture for about 0.05 to 20 minutes. In
the first stage, mainly hemicellulose and some cellulose are hydrolyzed
to sugars. The reaction vessel is then rapidly depressurized to flash off
the hydrolysate. Next, the residue is treated again in the second stage
with dilute mineral acid, heated to about 210° C. to 250°
C. and pressurized to maintain a liquid phase for about 0.05 to 20
minutes. The reactor is then rapidly depressurized to flash off the
hydrolysate to produce the sugars.

[0022]A reaction of these sugars with an acid catalyst then results in
5-hydroxymethyl-2-furfural (HMF) via a dehydrocyclization, as described
in Zhao et al., Science, Jun. 15, 2007, 316, 1597-1600; and Bicker et
al., Green Chemistry, 2003, 5, 280-284, which are incorporated herein by
reference. In Zhao et al., the sugar is treated with a metal salt such as
chromium(II) chloride in the presence of an ionic liquid at 100°
C. for three hours to result in 70% yield of HMF. In Bicker et al.,
sugars are dehydrocyclized to HMF by the action of sub- or super-critical
acetone as the solvent and sulfuric acid as the catalyst, at temperature
greater than 180° C. for about two minutes to yield HMF at nearly
70% selectivity.

[0023]The HMF is then readily oxidized to FDCA, as described by Merat et
al. in FR 2669634, which is incorporated herein by reference. In Merat et
al., a platinum-lead catalyst is used in the presence of oxygen and
aqueous alkaline conditions to oxidize HMF to FDCA at room temperature
(approximately 25° C.) for two hours to achieve a complete
conversion of the HMF, and an FDCA yield after acidification of 94%, with
a purity of about 99%.

[0024]In another embodiment of the invention, FDCA may be synthesized by
any conventional method from a non-biomass source, such as by the in situ
oxidation of HMF as described in Kroger et al., Topics in Catalysis,
2000, 13, 237-242; the oxidation by silver-copper reagent, as described
in U.S. Pat. No. 3,326,944; and the electrochemical oxidation to FDCA, as
discussed by Grabowski et al., PL 161831, which are incorporated herein
by reference. Such a non-biomass source may include, but is not limited
to, 2,5-dimethylfuran.

[0025]Suitable solvents which may be used in the practice of the invention
with FDCA include water, dimethylsulfoxide, N-methyl-2-pyrrolidinone,
N,N-dimethylformamide, C1 to C10 alcohols, C2 to C6
ketones, and C2 to C10 esters. Water is the preferred solvent.
Additives, such as alkaline and alkaline earth metal hydroxides, may also
optionally be used in the water to convert the FDCA into more
water-soluble salts and enhance the reactivity of the FDCA. Suitable
alkaline and alkaline earth metal hydroxides include sodium, potassium
and calcium hydroxides. The concentration of FDCA in the solvent is
typically in the range of about 5 to about 20 weight percent FDCA.

[0026]When FDCA is reacted with ethylene in the presence of a solvent, the
intermediate, bicyclic ether that is produced is
7-oxa-bicyclo[2.2.1]hept-2-ene-1,4-dicarboxylic acid. Ethylene may be
sparged or bubbled into a solution of FDCA. The amount of ethylene should
be in excess of the amount of FDCA and preferably, at least 2 moles of
ethylene per mole of FDCA.

[0027]In another aspect of the present invention, the
2,5-furandicarboxylate that may be used is dimethyl2,5-furandicarboxylate
(DM FDCA), i.e., a dimethyl ester derivative of FDCA. Typically, DM FDCA
can be derived by a reaction of FDCA and methanol in the presence of a
protic acid catalyst, such as concentrated sulfuric or phosphoric acid.
The FDCA is combined with methanol and phosphoric acid, and then heated
to approximately 200° C. under pressure to maintain a liquid phase
for about six to nine hours.

[0028]Suitable solvents which may be used in the practice of the invention
with DM FDCA include aromatic hydrocarbons, dimethylsulfoxide,
N-methyl-2-pyrrolidinone, N,N-dimethylformamide, C1 to C10
alcohols, C2 to C6 ketones, and C2 to C10 esters.
Toluene is a preferred solvent. The activity of the reaction may be
further enhanced by the addition of a catalytic amount of Lewis acids,
such as aluminum, boron, zinc or titanium salts, in the range of about 5
ppm to about 2000 ppm.

[0029]When DM FDCA is reacted with ethylene in the presence of a solvent,
the intermediate, bicyclic ether that is produced is
dimethyl7-oxa-bicyclo[2.2.1]hept-2-ene-1,4-dicarboxylate.

[0030]In another aspect of the present invention, the
2,5-furandicarboxylate that may be used is a mixture of FDCA and DM FDCA.
Suitable solvents which may be used in the practice of the invention with
the FDCA and DM FDCA mixture include water, aromatic hydrocarbons,
dimethylsulfoxide, N-methyl-2-pyrrolidinone, N,N-dimethylformamide,
C1 to C10 alcohols, C2 to C6 ketones, C2 to
C10 esters, and mixtures thereof.

[0031]The combination of the 2,5-furandicarboxylate and ethylene in the
presence of a solvent promotes a Diels Alder reaction to produce the
intermediate, bicyclic ether. The intermediate bicyclic ether is
7-oxa-bicyclo[2.2.1]hept-2-ene-1,4-dicarboxylate.

[0032]When the intermediate, bicyclic ether is produced, a spontaneous
dehydration reaction of the bicyclic ether will occur if the temperature
from the reaction of FDCA with ethylene is maintained so that the heat of
reaction is sufficient to drive the dehydration. A preferred temperature
at which the reaction system is maintained in order to drive the
dehydration is at least about 100° C. and, more preferably, about
200° C. This spontaneous dehydration allows for the production of
TA from the 2,5-furandicarboxylate in one step, i.e., the TA can be
produced in a single reactor since the dehydration of the bicyclic ether
can be caused to occur automatically without having to isolate the
bicyclic ether in a separate vessel.

[0033]In another aspect of the present invention, the bicyclic ether may
be isolated by any conventional method, such as filtration, and then
dehydrated via an acid-catalyzed dehydration reaction by dissolving the
bicyclic ether in a solvent such as acetic acid and heating to boil, to
enhance the ease of purification of the final TA product. The
acid-catalyzed dehydration reaction is generally known to those having
ordinary skill in the art to which this invention pertains. The
purification may be performed by recrystallization from a solvent, such
as water, in which the TA is soluble, as well as by other known
procedures.

[0034]The temperature of both the reaction of the 2,5-furandicarboxylate
with ethylene and the dehydration of the bicyclic ether should be
maintained in the range of about 100° C. to about 250° C.
and, preferably, in the range of about 180° C. to about
210° C. The ethylene is reacted with the 2,5-furandicarboxylate at
a pressure in the range of about 10 pounds per square inch gauge (psig)
to about 2000 psig. More preferably, the ethylene pressure is in the
range of about 50 psig to about 1000 psig, with about 100 psig to about
300 psig being most preferred. The 2,5-furandicarboxylate should be
reacted for about 60 minutes to about 480 minutes and, preferably, for
about 90 minutes to about 120 minutes.

[0035]The TA may be recovered by cooling the reaction mixture to ambient
temperature, and then filtering the solids from the supernatant.

[0036]The process of the present invention effectively produces TA without
the use of a conventional alkyl aromatic feedstock, such as paraxylene.
By reacting a 2,5-furandicarboxylate with ethylene in the presence of a
solvent to produce a bicyclic ether; and then dehydrating the bicyclic
ether, the inventor has surprisingly discovered that a high purity TA
composition is produced. In fact, the purity of the TA is comparable to
that of conventional PTA purified by hydrogenation of crude product from
paraxylene oxidation and is sufficient for direct conversion by reaction
with at least one glycol to polyester suitable for the manufacture of
fiber and film without the need for any additional purification.

[0037]Also, the inventive process does not produce partial oxidation
products commonly generated as byproducts in conventional paraxylene
oxidation processes. These byproducts include 4-carboxybenzaldehyde and
other contaminants, such as p-toluic acid, p-tolualdehyde, and benzoic
acid, all of which are commonly found in commercial PTA processes. Carbon
oxides normally associated with the decomposition of acetic acid are also
substantially absent (i.e., there may be trace levels of carbon dioxide
produced from a decarboxylation reaction of the 2,5-furandicarboxylate)
from the current process, as are the color bodies produced during the
liquid-phase oxidation of paraxylene.

[0038]Additionally, utilizing a 2,5-furandicarboxylate as an alternative
feedstock in the present invention allows for the production of TA
without the use of acetic acid, catalysts or oxygen, all of which are
found in conventional PTA processes. It should be noted that although
catalysts are not required in the practice of this invention,
non-conventional catalysts having Lewis acidity including, but not
limited to, zinc(II) salts, such as zinc(II) acetate or bromide, and
iron(III) salts, such as iron(III) acetate, may be used to improve
reaction rates. Moreover, utilizing a 2,5-furandicarboxylate allows for
the use of a renewable feedstock for the production of TA.

[0040]The following examples are intended to be illustrative of the
present invention and to teach one of ordinary skill how to make and use
the invention. These examples are not intended to limit the invention or
its protection in any way.

Example 1

[0041]5 grams of FDCA (available from the Atlantic Chemical Company) and
100 grams of distilled and deionized (D&D) water were combined in an
autoclave and then pressurized with ethylene and heated for 120 minutes.
After the reaction time elapsed, the unit was cooled and depressurized,
and the reaction mixture (i.e., a mixture of solids covered by the
reaction solvent, which is known as the "mother liquor") was collected.
This mixture was then separated by filtration to yield a filtered cake
(i.e., solids) and the mother liquor. Both the filtered cake and mother
liquor were analyzed by high pressure liquid chromatography (HPLC).

[0042]As shown below in Table 1, as the reaction conditions were made more
severe by increasing the temperature and pressure, not only was TA
produced in one step, i.e., in a single reactor vessel, but its yield was
also increased. Under the mild conditions of Example No. 1A, where 100
psig ethylene was used at a temperature of 100° C., no TA was
observed by HPLC analysis after 120 minutes. In Example No. 1B,
increasing only the temperature to 150° C. did produce a trace
concentration of TA in the mother liquor. By increasing only the pressure
from 100 to 200 psig, while holding the temperature at 100° C. in
Example No. 1C, the TA concentration in the mother liquor was increased.
By further increasing the ethylene pressure and temperature in Example
No. 1D to 200 psig and 200° C., respectively, the filtered cake
was found to contain a measurable TA level of 372 ppmw. Lastly, in
Example No. 1E, the FDCA charge was increased from 5 to 10 grams, and the
ethylene pressure was further increased to 250 psig, while holding the
temperature at 200° C. No insoluble solids were observed in the
reaction mixture. A sample of the homogeneous liquid material was
obtained and permitted to dry to leave behind solids that had once been
soluble in the homogeneous liquid. The total solids concentration, which
was determined by weighing the residue of the evaporated sample, dividing
by the total weight of the mother liquor, and multiplying by 100, was
4.2785 wt %. Of the evaporated residue, it was found to contain 3,504
ppmw TA.

[0043]Based on these results and the amount of FDCA charged, it was
estimated that the TA was made in 0.14 mol % yield. The presence of
7-oxa-bicyclo[2.2.1]hept-2-ene-1,4-dicarboxylic acid was also observed by
HPLC analysis. Thus, as demonstrated in Table 1, the inventive process
successfully produced TA from FDCA. In addition, because paraxylene was
not used, the TA was produced in the absence of 4-carboxybenzaldehyde and
color bodies normally associated with paraxylene oxidation.

[0044]100 grams of FDCA, 800 grams of methanol, 9.41 grams of phosphoric
acid (85%), and 1.26 grams of water were charged into a high pressure
reactor equipped with a gas inlet and outlet. The reactor was sealed,
filled and flushed with nitrogen nine times. The inlet and outlet were
then closed and the reaction mixture was stirred and heated to
200° C. for nine hours. The reactor was cooled, vented, and 878.95
grams of the total reactor content were collected. A gas-chromatographic
analysis was conducted on the solids to reveal the following gas
chromatographic peak area percentages: 63% DM FDCA, 21% monomethyl FDCA,
and 14.9% unreacted FDCA. There were 1.1% unknowns estimated to be
present.

[0045]The DM FDCA was separated from the other components by filtration of
the solids. The solids were washed twice with fresh methanol and then
dried at 60° C. under a slight vacuum at 27 mmHg to produce about
44.813 grams of solids. This material was then analyzed by gas
chromatography--mass spectrometry to reveal the following normalized peak
areas: 95.0% DM FDCA, 3.2% monomethyl FDCA, and 1.90% FDCA.

[0046]5 grams of DM FDCA and 60.5 grams of toluene were added into a Parr
reactor. The reactor was sealed and pressurized with ethylene to 250
psig. The mixture was heated with stirring to 120-125° C., and
then held for about seven hours. The reactor was cooled and
depressurized, and 60.125 grams of total reactor effluent were collected.
The slurry was filtered, and the solids were initially dried overnight at
65 to 70° C. under ambient pressure, and then dried at 100°
C. and under vacuum at 27 mmHg for 30 minutes. Analysis of the filtered
solids revealed the following components and their corresponding
concentrations in weight percent: 39.7% DM FDCA, 0.699% monomethyl FDCA,
0.011% FDCA, and 0.015% TA.

[0047]This procedure was repeated, except that the temperature was fixed
at 190-195° C. for approximately five hours. Analysis of the
solids revealed the following concentrations in weight percent: 39.1% DM
FDCA, 0.547% monomethyl FDCA, 0.21% FDCA, and 0.021% TA.

[0048]Based on these results, the inventive process successfully produced
TA from DM FDCA and, surprisingly, no dimethyl terephthalate was
produced. One skilled in the art would have expected the dimethyl ester
to remain as part of the molecule throughout the reaction sequence. In
addition, because DM FDCA was used as the feedstock, rather than a
conventional alkyl aromatic, the TA was produced in the absence of carbon
oxides normally associated with solvent decomposition, impurities and
color bodies. Furthermore, these findings revealed that FDCA can be used
directly or as an ester derivative to produce the desired product, TA.

[0049]While the present invention is described above in connection with
preferred or illustrative embodiments, these embodiments are not intended
to be exhaustive or limiting of the invention. Rather, the invention is
intended to cover all alternatives, modifications and equivalents
included within its spirit and scope, as defined by the appended claims.